Faceted light pipe

ABSTRACT

A light pipe used for backlighting liquid crystal displays has a planar front surface and a stairstepped or faceted back surface. Light is injected from the ends of the light pipe from cold or hot cathode, apertured, fluorescent lamps. The cold cathode lamps are preferably insulated to raise their operating temperature. The back surface has a series of planar portions parallel to the front surface connected by facets, which are angled so that the injected light reflects off the facets and through the front surface. A reflector having a planar, highly reflective, highly scattering surface or a sawtoothed or grooved upper surface is located adjacent to and parallel with the light pipe back surface to reflect light escaping from the back surface back through the light pipe to exit the front surface. The axis of grooves is preferably slightly skewed from the facet axis to reduce moire pattern development. A low scattering or loss diffuser is located adjacent to and parallel with the light pipe front surface to reduce moire pattern development. The liquid crystal display is located over the low scattering diffuser. A separate injector may be located between the lamp and the light pipe to better couple the light into the light pipe.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to backlighting systems used with liquid crystaldisplays, and more particularly to light pipe systems.

2. Description of the Related Art

Liquid crystal displays (LCD's) are commonly used in portable computersystems, televisions and other electronic devices. An LCD requires asource of light for operation because the LCD is effectively a lightvalve, allowing transmission of light in one state and blockingtransmission of light in a second state. Backlighting the LCD has becomethe most popular source of light in personal computer systems because ofthe improved contrast ratios and brightnesses possible. Becauseconventional monochrome LCD's are only approximately 12% transmissiveand color LCD's are only approximately 2% transmissive, relative largeamounts of uniform light are necessary to provide a visible display. Ifpower consumption and space were not of concern the necessary level anduniformity of backlight could be obtained.

However, in portable devices power consumption, which directly effectsbattery life, and space are major concerns. Thus there is a need toobtain a sufficiently uniform and bright backlight level with as littlepower as possible in as little space as possible at, of course, as low acost as possible.

Numerous designs exist which trade off various of these goals to achievea balanced display. Several of these designs, such as light curtains andlight pipes, are shown in the figures and will be described in detaillater. The designs generally trade off uniformity of backlighting forspace or efficiency. The designs utilize various scattering means and afinal diffuser before the light is presented to the LCD. The scatteringmeans and the diffusers both allow loss of light and thus reduce theefficiency of the transfer from the light source to the LCD. While thedesigns are adequate in some cases, the demands for longer battery lifewith monochrome LCD's or equal battery life with color LCD's arepresent, as is a desire for the use of less space.

SUMMARY OF THE INVENTION

The present invention is a faceted, parallel surface light pipe design.Light sources, preferably reflector or apertured fluorescent lamps, butalternatively uniform lamps, supply light to one or both ends of a lightpipe. The front surface of the light pipe, on which is positioned a lowloss diffuser, which in turn is in contact with the LCD, is planar,while the back surface of the light pipe is generally parallel to thefront surface, but has a stair stepped or faceted surface. The facetsare preferably formed at an angle so that the light injected into theends of the light pipe is reflected off the facets and through the frontsurface. The pitch or step length of the facets is such that thefaceting structure is not visible to the human eye. The step height ofthe facets is preferably in the micron range and may increase with thedistance from the lamp. A planar, white, diffuse reflector, which ishighly reflective and high scattering, is positioned parallel to theback surface of the lightpipe. This allows light leaving the backsurface to be reflected back through the front surface of the lightpipe. Alternatively, the reflector can have a sawtoothed or groovedsurface. The axis of the sawtooth ridges is preferably slightly askewthe axis of the facets to reduce the effects of moire patterndevelopment. The reflections can be satisfactorily controlled so thatlittle light is returned to the light source, little light leaves theother end of the light pipe and little light is trapped in the lightpipe.

This design is in contrast to the low efficiency of the variousscattering techniques of the prior art which allow the losses described.The pitch and step height are sufficient so that a conventional diffuseris not required before the LCD, thus allowing further relative increasedlight transmission and efficiency. However, a low loss diffuser ispreferably located between the light pipe and the display to overcomemoire pattern development. Various designs of the end of the light pipeand the actual facet profile and pitch can be used to alter specificaspects of the transmission to vary the light output.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the prior art and the present invention can beobtained when the following detailed description of the preferredembodiment is considered in conjunction with the following drawings, inwhich:

FIGS. 1-4 are views of various backlighting systems of the prior art;

FIG. 5 is a view of a backlighting system according to the presentinvention including a light pipe and light sources;

FIGS. 6 and 7 are greatly enlarged views of portions of the backlightingsystem of FIG. 5;

FIGS. 8, 9A, 9B and 10 are greatly enlarged views of portions of thelight pipe of FIG. 5 showing light action;

FIG. 11 is a greatly enlarged view of an alternate injector according tothe present invention;

FIG. 12 is a greatly enlarged, view of a facet of the light pipe of FIG.5;

FIG. 13 is an alternate single source backlighting system according tothe present invention; and

FIGS. 14 to 17 are alternative designs for a lamp reflector according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Prior to discussing the present invention, it is considered appropriateto further discuss various designs in the prior art to explain thepresent technology and thus make clear the scope of the presentinvention.

FIG. 1 generally discloses a conventional light curtain system used inproviding backlight to an LCD. Two uniform output cold cathodeflorescent lamps 20 and 22 are the basic light source for the system S1.A reflector 24 generally having a white reflective surface facing thelamps 20 and 22 is used to redirect the light being emitted by the lamps20 and 22 in directions other than towards the LCD D. A light blockinglayer 26 is used to reduce any hot, nonuniform spots which would occurdirectly over the lamps 20 and 22 to provide a first level of uniformityto the light. The blocking layer 26 is preferably formed of a variableopacity mylar material, with the material being very opaque near thelamps 20 and 22 and becoming more translucent or transparent away fromthe lamps. This variable opacity is generally provided by a printedpattern on the surface of the blocking layer 26. However, because thelight is not sufficiently uniform after passing through the blockinglayer 26, a diffuser 28, which is generally a translucent plasticmaterial, is used to further diffuse the light and produce a moreuniform display. However, the diffuser generally reduces the lighttransmission by approximately 10% to 50%, which greatly reduces theefficiency of the overall backlighting system S1. The light curtainsystem S1 is relatively thick and as the lamps are placed closer to theblocking layer alignment problems increase, reducing the capability toeconomically manufacture the system S1.

Two variations of similar light pipe systems are shown in FIGS. 2 and 3and are generally referred to as systems S2 and S3. Both systems againgenerally use uniform emission lamps 20 and 22, but the lamps arelocated at the ends of a light pipe 30. White reflectors 32 and 34 areprovided around the lamps 20 and 22 so that the uniform light isdirected into the light pipe 30. The light pipe 30 includes a variabledensity scattering structure so that the light is projected out thefront surface 36 of the light pipe 30, through the diffuser 28 andthrough the LCD D. In the backlighting system S2 the light pipe 30 usestitanium oxide particles or other particles located in the light pipe 30to perform the scattering function. Preferably the density of theparticles is greater near the center of the display and lesser near theends of the display near the lamps 20 and 22 to produce a uniform lightbecause of the effective light density, which reduces approaching thecenter of the light pipe 30. A mirrored or fully reflective surface 38is applied to the back surface 37 of the light pipe 30 so that any lightwhich is scattered in that direction is reflected in an attempt to havethe light transmitted through the front surface 36 of the light pipe 30.However, this light might again be scattered and so various losses canoccur. The backlighting system S3 uses a scattering structure printed onthe front surface 42 of the light pipe 40 to provide the scatteringeffect. In both systems S2 and S3 a diffuser 28 is required to provide asufficiently uniform light source to the LCD D. In these designs lightcan become trapped in the light pipe 40 and can readily be transmittedfrom one end to the other and thus be lost, reducing overall efficiency.

An alternate prior art light pipe design is shown in FIG. 4, and isgenerally referred to by S4. In this case a double quadratic wedge lightpipe 44 is used in contrast to the parallel light pipes 30 and 40 of thesystems S2 and S3. The back surface 46 of the light pipe 44 is arelatively constant, diffuse surface, with the front surface 47 being aclear or specular surface. The curve formed by the back surface 46 is aquadratic curve such that more light which impinges on the back surfacesis reflected through the front surface as the light approaches thecenter of the light pipe 44. In this way a relatively uniform lightsource can be developed, but a diffuser 28 is still required to providean adequately uniform source. This design has problems in that somelight does leak out at low angles out the back and in some cases lightis sent back to the source. Additionally, there are some problems at theexact center of the display.

Thus while the light pipe designs S2, S3 and S4 are generally thinnerdesigns than the light curtain system S1, they have problems related tohaving to turn the light generally ninety degrees and thus have a lowerefficiency than the light curtain design, which in turn has the drawbackit is a relatively thick design which limits the design possibilities inportable computer systems and television applications.

A backlight system according to the present invention, generallyreferred to as S5, is shown in FIG. 5. A faceted, dual source light pipe100 is coupled to an LCD D. FIG. 5 shows two alternate lamp variations.In one variation a uniform dispersion lamp 102 may be located adjacentto an optional separate injector 104. The lamp 102 is preferablysurrounded by a reflector 106. The separate injector 104 is used tocouple the transmitted light from the lamp 102 into the light pipe 100.The second and preferred embodiment of the light source is a lamp 108which is a cold cathode, reflector florescent lamp having an aperturelocated adjacent to the end 105 of the light pipe 100. A reflector 106may be used with the lamp 108. For use with monochrome displays D a coldcathode lamp is preferred to keep power consumption at a minimum, thebacklight S5 being sufficiently efficient that the added light output isnot considered necessary. However, if a color display D is used, a hotcathode lamp is preferred because of the need for maximum light output.Additionally, a reflector lamp is preferred to an aperture lamp forlamps of the diameter preferably being used in the preferred embodiment.A reflector lamp has a first internal coating of the reflectivematerial, which then has an aperture developed and is finally completelyinternally coated with phosphor. The aperture lamp is first coatedinternally with the reflective material, then with the phosphor andfinally the aperture is developed. Given the relatively large arc of theaperture, the additional phosphor present in the reflector lamp morethan offsets the lower brightness because the light must travel throughthe phosphor coating the aperture. An index matching material 107 mayoptionally be provided between the lamp 108 and the light pipe 100.

As shown the upper surface of the light pipe 100 is planar, specular andis adjacent a low trapping and low scattering diffuser 111. The diffuser111 preferably produces less than 10% brightness drop and is used toreduce the effects of any moire pattern developed between the light pipe100 and the LCD display D because of the pitch and alignment variationsbetween the items. The LCD display D is located over the diffuser 111. Aback surface reflector 126 is located parallel to the back surface 112of the light pipe 100 to reflect light through the back surface 112 backthrough the light pipe 100 and out the front surface 110. In themacroscopic view of FIG. 5 the back surface 112 of the light pipe 100appears to be a straight wedge or planar surface but in the enlargedviews shown in FIGS. 6 and 7 the stair stepped or faceted structure isclearly shown.

The back surface 112 consists of a series of portions 114 parallel withthe front surface 110, with a series of facets 116 leading to the nextparallel portion 114. FIG. 6 is the enlarged view showing the couplingof the apertured lamp 108 with the light pipe 100, while FIG. 7 showsthe central portion of a dual source light pipe 100. Preferably the lamp108 is a fluorescent type lamp with an aperture height approximating thethickness of the light pipe 100. The light pipe 100 preferably has athickness of 5 mm or less at the outer edges and a thickness of 1 mm inthe center. The thickness of 1 mm is preferred because the light pipe100 is preferably made of polymethyl methacrylate (PMMA) and so thisminimum thickness is provided for mechanical strength reasons. Othermaterials which can develop and maintain the faceted structure may beused to form the light pipe 100. The light pipe 100 is restrained to athickness of approximately 5 mm so that when combined with the LCD D,the reflector 126 and the diffuser 111 of the preferred embodiment, theoverall unit has a thickness of less than 1/2 of an inch, not countingthe lamp 108, thus saving a great deal of space as compared to prior artlight curtain designs. The lamp 108 can have a diameter greater than thethickness of the light pipe 100, allowing a narrower aperture, as shownin FIGS. 5 and 6, or preferably can have a diameter approximately equalto the thickness of the light pipe 100 as shown in FIGS. 5 and 11, withan angularly larger aperture.

If the preferred cold cathode lamp is used as the lamp 108, the lamp 108may run at temperatures below the optimum efficiency temperature becauseof the small size of the lamp 108. Therefore it is preferable to use areflector 106 which is also insulating. Four alternate embodiments areshown in FIGS. 14-17. In the embodiment of FIG. 14, a U-shaped insulator150 is used. Inside the insulator 150 and before the light pipe 100 canbe a white reflective material 152. This material 152 can be adhesivelyapplied if needed, but preferably the insulator 150 is formed of awhite, reflective material. The presently preferred material is a highdensity polystyrene foam, but silicone, polyethylene, polypropylene,vinyl, neoprene or other similar materials can be used. A double sidedadhesive layer 154 is used to retain the insulator 150 to the light pipe100. The insulator 150 traps the heat produced by the lamp 108, thusraising the lamp operating temperature and, as a result, its efficiency.It is desireable that the insulator 150 and associated materials be ableto withstand 100° C. for extended periods and have a moderate fireresistance.

In the variation of FIG. 15, an expanded polystyrene block 156, orsimilar material, is combined with two strips of foam tape 158 to formthe insulating reflector 106. Preferably the adhesive surface of thetape 158 includes a mylar backing for strength. In the variation of FIG.16 foam tape 158 is again used, but this time longitudinally with thelamp 108 to form a U-shape. Preferably the inside of the U is covered bya reflective tape 160, while the foam tape 158 is fixed to the lightpipe 100 by a double sided metallized mylar tape 162.

Yet another variation is shown in FIG. 17. A clear acrylic material 164surrounds the lamp 108 and is attached to the light pipe 100 by asuitable adhesive layer. The outer surface 166 of the acrylic material164 is coated with metallizing material 168 so that the outer surface166 is a reflector. In this manner light which is emitted from the lamp108 at locations other than the aperture is reflected through theacrylic material 164 into the light pipe 100, instead of through thelamp 108 as in FIGS. 14 to 16. While the acrylic material 164 willprovide some insulation, it may not be sufficient to raise the lamp 108temperature as desired and so foam insulating tape 158 may be used overthe acrylic material 164 for better insulation. In this case the entireinner surface of the foam tape 158 may be adhesive coated as thereflective layer is present on the acrylic material 164.

A separate injector 104 may be used to couple the light being emitted bythe lamp 108 into the light pipe 100, but preferably the end 105 of thelight pipe 100 is considered the injector. The injector 104 or end 105is preferably a flat surface which is polished and specular, that isnon-diffuse, and may be coated with anti-reflective coatings. A flat,specular surface is preferred with a light pipe material having an indexof refraction greater than 1.2, which results in total internalreflection of any injected light, which the facet structure will projectout the front surface 110.

Several other alternatives are available for the injector, such as indexmatching material 107 to match the lamp 108 to the light pipe 100 toeliminate surface reflections. The index matching material 107 is aclear material, such as silicone oil, epoxy or polymeric material, whichcontacts both the lamp 108 and the end 105. Alternatively, the injector118 can be shaped to conform to the lamp 108 with a small air gap (FIG.11). This curved surface of the injector 118 helps locate the lamp 108.Additionally, a cylindrical fresnel lens can be formed on the end 105 orseparate injector 104 to help focus the light being emitted from thelamp 108. Its noted that a cylindrical fresnel lens is preferred over atrue cylindrical lens to limit leakage of the light. Alternate lensescan be developed on the separate injector 104 or end 105 which incombination with the facets 116 can effect the output cone of the lightas it exits the light pipe 100. Preferably the output cone is the sameas the viewing angle of the LCD D so that effectively no light is beinglost which is not needed when viewing the LCD D, thus increasingeffective efficiency of the system.

FIG. 8 shows a greatly enlarged view of a portion of one facet 116 andseveral parallel portions 114 of the light pipe 100. As can be seen theparallel back surface portions 114 are parallel with the front surface110, both of which are specular, so that the light pipe 100 preferablyutilizes only specular reflections and does not utilize diffusereflection or refraction, except in minor amounts. By having primarilyonly specular reflections it is possible to better control the light sothat it does not leave the light pipe 100 in undesired directions, thusallowing better focusing and less diffusion. Thus the basic propagationmedia of the light pipe 100 is that of a parallel plate light pipe andnot of a wedge or quadratic. The facet 116 preferably has an angle α of135 degrees from the parallel portion 114. This is the preferred anglebecause then light parallel to the faces 110 and 114 is transmittedperpendicular to the light pipe 100 when exiting the front face 110.However, the angle can be in any range from 90 to 180 degrees dependingupon the particular output characteristics desired. The pitch P (FIG. 6)or distance between successive facets 116 is related to and generallymust be less than the visual threshold of the eye which, whileproportional to the distance the eye is from the LCD D, has preferredvalues of 200 to 250 lines per inch or greater. In one embodimentwithout the diffuser 111 the pitch P is varied from 200 lines per inchat the ends of the light pipe 100 near the lamps 108 to 1000 lines perinch at the center so that more reflections toward the front face 110occur at the middle of the light pipe 100 where the light intensity hasreduced. The pitch in the center is limited to 1,000 lines per inch toprovide capability to practically manufacture the light pipe 100 inlarge quantities, given the limitations of compression or injectionmolding PMMA. If the diffuser 111 is utilized, the pitch can go lowerthan 200 lines per inch because of the scattering effects of thediffuser 111. The limit is dependent on the particular diffuser 111utilized. Thus the use of the diffuser 111 can be considered as changingthe limit of visual threshold. In one embodiment of the presentinvention the facet height H (FIG. 8) ranges from approximately I micronnear the end 105 to 10 microns near the middle, the farthest point froma lamp. In the drawings the facet height is greatly enlarged relative tothe pitch for illustrative purposes. The preferred minimum facet heightis 1 micron to allow the light pipe 100 to be developed usingconventional manufacturing processes, while the preferred maximum facetheight is 100 microns to keep overall thickness of the light pipe 100reduced. It is noted that increasing the facet height of a facet 116 atany given point will increase the amount of light presented at thatpoint, referred to as the extraction efficiency, so that by changing thepitch P, facet height H and facet angle α varying profiles andvariations in uniformity of the light output from the front surface 110can be developed as needed.

While the desire is to use purely specular reflective effects in thelight pipe 100, some light will be split into transmitted and reflectedcomponents. Even though there is total internal reflection of lightinjected into the light pipe 100 by the front surface 110 and parallelportions 114, when the light strikes a facet 116 much of the light willexceed the critical angle and develop transmitted and reflectedcomponents. If the light is reflected from the facet 116, it willpreferentially be transmitted through the front surface 110 to theviewer. However, the transmitted component will pass through the backsurface 112. Thus a reflective coating 122 may be applied to the facet116. This reflective material 122 then redirects any light transmittedthrough the facet 116. This is where the greatest amount of transmissionis likely to occur because of the relatively parallel effects asproceeding inward on the light pipe 100.

A design trade off can be made here based on the amount of lightexceeding the critical angle being reflected back from the front surface110, through the back surface 112 or through the facets 116. If there isa greater amount of this light which will be transmitted out the backsurface 112 and lost, it may be desirable to fully coat the back surface112 as shown in FIG. 10 so that the entire back surface 112 is coated bya reflector material 124. Because the reflector material is preferablyaluminum or other metals the efficiency of the reflector 124 is not 100%but typically in the range of 80% to 90%, some reflective loss occurs ateach point. Thus there is some drop in efficiency at each time the lightimpinges on the reflector 124, but based on the amount of high anglelight present, more light may actually be transmitted through the frontsurface 110, even with the reflective losses. If the lamp transmits muchmore parallel light, then the coating of the parallel portions 114 withreflective material may not be necessary.

In the embodiments shown in FIGS. 9A and 9B no reflective coatings areactually applied to the light pipe 100 but instead a reflector plate126A or 126B is located adjacent the back surface 112 of the light pipe100. In the preferred embodiment shown in FIG. 9A, the reflector plate126A is planar and has a white and diffuse surface 170 facing the backsurface 112 of the light pipe 100. The surface 170 is highly reflectiveand high scattering to reflect the light passing through the backsurface 112 back through the light pipe 100 and out the front surface110. The thickness of the reflector plate 126A is as needed formechanical strength.

In an alternate embodiment shown in FIG. 9B, the front or light pipefacing surface 132 of the reflector plate 126B has a sawtoothed orgrooved surface, with the blaze angle β of the sawtooth being in therange of 30 to 60 degrees, with the preferred angle being approximately40 degrees. The pitch W of the sawteeth is different from the pitch P ofthe light pipe facets to to reduce the effects of moire patterndevelopment between the light pipe 100 and the reflector 126B. Thepitches are uniform in the preferred embodiment and are in the range of1-10 mils for the facets and 1-10 mils for the reflector grooves, withthe preferred facet pitch P being 6 mils and the sawtooth pitch W being4 mils. The sawtooth pitch W can be varied if the facet pitch P varies,but a constant pitch is considered preferable from a manufacturingviewpoint. The thickness of the reflector plate 126B is as needed formechanical support.

Additionally, the longitudinal axis of the sawteeth is slightly rotatedfrom the longitudinal axis of the facets to further reduce the effectsof moire pattern development. The sawtooth surface 132 is coated with areflecting material so that any impinging light is reflected backthrough the light pipe 100 as shown by the ray tracings of FIG. 9.Further, the sawteeth can have several different angles between thepreferred limits to better shape the light exiting the light pipe 100.

The majority of the light which impinges on the sawtooth surface 132 orthe diffuse surface 170 will proceed directly through the light pipe 100and emerge from the front face 110 because the light pipe 100 iseffectively a parallel plate because the facet area is only a very smallpercentage as compared to the flat portion of the back surface 112. Thusthe light which exits the back surface 112 of the light pipe 100 isreflected back through the light pipe 100 to exit the front surface 110and contribute to the emitted light with little loss.

Additionally, the actual facet profile 116 is not necessarily planar. Asshown in FIG. 12, the actual facet profile may be slightly concave 128or slightly convex 130. The facets 116 then form a lenticular array andcan be curved as desired to help tailor the output profile of the lightcone. Additionally, the facet 116 surface may be roughened to increasescattering if desired.

While the design of the light pipe 100 illustrated in FIG. 5 use lampsat both ends in a dual light source arrangement, light could be providedfrom only one end in a single source configuration as shown in FIG. 13.The end opposite the light source 102 is then the thinnest portion ofthe light pipe 100' and a reflective surface 134 is provided to limitlosses from the end of the light pipe 100'. The light pipe 100' stillhas the planar front surface 110, a faceted back surface 112, areflector plate 126 and a low loss diffuser 111 and the other variationsdescribed above are applicable. The facet pitch and height arepreferably varied as previously described to develop greater lightredirection to help compensate for the lesser total amount of lightsupplied by the light source 102.

Having described the invention above, various modifications of thetechniques, procedures, material and equipment will be apparent to thosein the art. It is intended that all such variations within the scope andspirit of the appended claims be embraced thereby.

We claim:
 1. A system for backlighting a liquid crystal display, comprising:a light pipe having a generally planar front surface for providing light to the liquid crystal display, having a faceted back surface wherein said back surface includes a plurality of generally planar portions parallel to said front surface and a plurality of facets formed at an angle to said front surface and located connecting said back surface parallel portions, and having at least one end surface for receiving light to be transmitted through said front surface; light source means located adjacent each said end surface for receiving light of said light pipe for providing light to said light pipe; and reflector means located adjacent to and generally parallel to said light pipe back surface for reflecting light back through said light pipe.
 2. The system of claim 1, wherein said reflector means is generally planar and has a front surface adjacent to said light pipe back surface, said reflector means front surface including a series of grooves, the longitudinal axis of said grooves extending somewhat parallel to the longitudinal axis of said facets.
 3. The system of claim 2, wherein the longitudinal axis of said grooves is somewhat askew of the longitudinal axis of said facets.
 4. The system of claim 1, wherein said reflector means is generally planar and has a front surface adjacent to said light pipe back surface, said reflector means front surface being highly reflective and highly scattering.
 5. The system of claims 3 or 4, further comprising:injector means between said light source means and said light pipe for coupling light produced by said light source means to said light pipe.
 6. The system of claim 5, wherein said injector means has a flat surface facing said light source means.
 7. The system of claim 6, wherein said injector means flat surface is coated with an anti-reflective coating.
 8. The system of claim 5, wherein said injector means includes index matching material located between and contacting said light source means and said light pipe.
 9. The system of claim 5, wherein said injector means is shaped to generally conform to the surface of said light source means.
 10. The system of claim 5, wherein said injector means includes a surface having a fresnel lens developed thereon.
 11. The system of claim 10, wherein said fresnel lens is a cylindrical fresnel lens.
 12. The system of claims 3 or 4, wherein each said end for receiving light of said light pipe has a flat surface.
 13. The system of claim 12, wherein said end is coated with an anti-reflective coating.
 14. The system of claim 12 wherein said end has a fresnel lens developed thereon.
 15. The system of claim 14, wherein said fresnel lens is a cylindrical lens.
 16. The system of claims 3 or 4, wherein each said end for receiving light of said light pipe is shaped to generally conform to the surface of said light source means.
 17. The system of claims 3 or 4, wherein said light source means includes fluorescent lamps.
 18. The system of claim 17, wherein said lamps are reflector lamps.
 19. The system of claim 17, wherein said lamps are aperture lamps.
 20. The system of claim 17, wherein said lamps are cold cathode lamps.
 21. The system of claim 20, wherein said lamps are partially encompassed by insulation.
 22. The system of claim 21, wherein said insulation includes a reflective surface facing said lamps.
 23. The system of claim 17, wherein said lamps are hot cathode lamps.
 24. The system of claims 3 or 4, wherein said light source means includes uniform dispersion fluorescent lamps.
 25. The system of claim 24, wherein said light means further includes reflectors formed around said lamps to reflect light to said light pipe.
 26. The system of claims 3 or 4, wherein said light pipe is formed of polymethyl methacrylate.
 27. The system of claims 3 or 4, wherein the angle of said facets from said parallel portion is between 90 and 180 degrees.
 28. The system of claim 27, wherein the angle is approximately 135 degrees.
 29. The system of claims 3 or 4, wherein the pitch defined by the distance from successive facets is less than that required to exceed the visual threshold of a human being.
 30. The system of claim 29, wherein said pitch is randomly varied.
 31. The system of claim 29, wherein said pitch is uniformly varied to a maximum of approximately 1000 per inch.
 32. The system of claims 3 or 4, wherein the facet height between successive parallel portions is varied between two limits.
 33. The system of claim 32, wherein said facet height limits are approximately 1 and 100 microns.
 34. The system of claims 3 or 4, further comprising a diffuser located adjacent to and generally parallel to said light pipe front surface.
 35. The system of claim 1, further comprising a low scattering diffuser located adjacent to and generally parallel to said light pipe front surface.
 36. The system of claims 3 or 4, wherein said facets are generally planar.
 37. The system of claims 3 or 4, wherein said facets are portions of a generally cylindrical surface. 